Horoka Tomamu Small Mammal Survey 2016















Grey red-backed vole (Myodes rufocanus)



The Horoka Tomamu Small Mammal Survey was conducted by Dr Dewa Hiroshi and Shimizu Shogo of the O-sara-pet Bat Research Center in Asahikawa, Hokkaido.




The catch-and-release survey was held on 15-17 September 2016, to follow up on another three years earlier (22-25 July 2013), which only found one animal (a small Japanese field mouse, Apodemus argenteus) in a year when there was a marked decline in small mammal populations. (The 2016 survey followed the same methodology as that of 2013.)




Corrugated galvanised iron traps and plastic snare cups were set on the first day, in five different areas (fig 1). Each area had a total of 20 traps and 5 plastic snare cups, each set at 10m intervals, baited with oats. The traps were checked each day and left for two days. Some hair was shaved from captured animals to identify them if they were re-caught. 


The density of animals was calculated per 100 Trap (T) per night (N).


Survey areas


Area 1: Flat near Horoka-Tomamu river

Elevation 499m.

Trees: Japanese elm (Ulmus davidiana var. japonica), Japanese white birch (Betula platyphylla), Manchurian alder (Alnus hirsuta), willows, Mongolian oak (Quercus mongolica)

Tree coverage: 42%

Ground coverage (sasa): 74%


Area 2: Lower south slope

Elevation 503 to 544m

Trees: Japanese elm (Ulmus davidiana var. japonica), Japanese white birch (Betula platyphylla), painted maple (Acer pictum), Sakhalin cork tree (Phellodendron sachalinense Sarg.), Mongolian oak (Quercus mongolica)

Tree coverage 50%). 

Ground coverage (sasa): 82.5%

There is Phragmites australis grass concentration around the path trailhead.


Area 3: Higher south side steep section, 

Elevation 584 to 657m. 

Trees: Japanese lime, Japanese elm (Ulmus davidiana var. japonica), Japanese white birch (Betula platyphylla), Manchurian ash (Fraxinus mandshurica), painted maple (Acer pictum), Manchurian alder (Alnus hirsuta), panicled hydrangea (Hydrangea paniculata)

Tree coverage: 59%

Ground coverage (mostly sasa): 93%


Area 4: Top of the hill and northern slope 

Elevation 611 to 662m.

Trees: Japanese white birch (Betula platyphylla) around the top. Sakhalin cork tree (Phellodendron sachalinense Sarg.), Ezo spruce (Picea jezoensis), Sakhalin fir (Abies sachalinensis), Japanese rowan (Sorbus commixta), forked viburnum (Viburnum furcatum), downy Japanese maple (Acer japonicum), Japanese bigleaf magnolia (Magnolia obovata)

Tree coverage: 57%

Ground coverage (sasa): 94%


Area 5: Lower northern side

Elevation 565 to 608m

Trees: Ezo spruce (Picea jezoensis), Sakhalin fir (Abies sachalinensis), Japanese yew (Taxus cuspidata), painted maple (Acer pictum), Japanese rowan (Sorbus commixta), Sakhalin cork tree (Phellodendron sachalinense Sarg.), Japanese white birch (Betula platyphylla), downy Japanese maple (Acer japonicum

Tree coverage: 55%

Ground coverage (sasa): 92%





The following were caught in traps:


5 grey red-backed voles (Myodes rufocanus), in areas 1 (2 voles), 4 (1 vole) and 5 (2 voles)

1 small Japanese field mouse (Apodemus argenteus), in area 5 


The following were caught in plastic cups:


3 long-clawed shrews (Sorex unguiculatus), in areas 2 (1 shrew) and 3 (2 shrews)  

1 Laxmann’s shrew (Sorex caecutiens), in area 4

1 slender shrew (Sorex gracillimus), in area 4


This compares to 2013, when six areas were set with traps and only one small Japanese field mouse was captured. 


In terms of density (100TN), this was 0.28 in 2013 and 3.0 in 2016. Density in other sites can vary considerably, up to 30.0 or more. 


As far as we know, this is the first time the slender shrew (Sorex gracillimus) has been found in the south Kamikawa/Tomamu area. 





We would like to thank Keisuke Nakata of the Administrative Agency Hokkaido Research Organisation for providing statistical information about small mammal population fluctuations in Hokkaido.



See also the htmfsurvey4.pdf (in Japanese).


Simon Holledge, 12 March 2017